Fuel supply method

ABSTRACT

The method of the present invention calculates based on the status of the exhaust emission purifier, a required supply of fuel to be supplied from the fuel supply valve to the exhaust passage, reads a unit fuel supply L U  in accordance with a energized time t U  for the fuel supply valve per one shot, supplies with a driving cycle depending on the required supply, fuel in the unit supply to the exhaust passage, when E DT −E DU &lt;E A −(L U −g) is established, the energized time t UT  corresponding to the target fuel supply is interpolated as a function of (L U /g) and the target fuel supply L U  is updated as a new unit supply L U , and the function of (L U /g) is supplied as a new energized time t U  from the fuel supply valve to the exhaust passage.

TECHNICAL FIELD

The present invention relates to a fuel supply method for allowing an internal-combustion engine including an exhaust emission purifier to efficiently perform the activation processing and the regenerating processing of the exhaust emission purifier.

BACKGROUND ART

In recent years, for complying with strict exhaust gas regulations applied to an internal combustion engine, it is necessary to activate an oxidation catalytic converter which comprises an exhaust emission purifier at the time of starting up the engine, or to maintain an activated status of the converter in an actuation of the engine. Therefore, Patent Literature 1 has proposed an internal combustion engine in which an exhaust gas heating system is incorporated in an exhaust passage upstream of the exhaust emission purifier. The exhaust gas heating system generates a burning gas in an exhaust gas, and supplies the generated burning gas to the exhaust emission purifier at the downstream thereof, thereby activating the purifier and maintaining the activated status thereof. Therefore, the exhaust gas heating system is generally provided with a fuel supplying valve for supplying fuel to the exhaust passage and an igniting unit such as a glow plug for heating the fuel to be ignited, thereby generating a burning gas.

CITATION LIST Patent Literature

-   PTL: Japanese Patent Laid-open No. 2010-059836

SUMMARY OF INVENTION Technical Problem

When controlling the fuel supplied from a fuel supply valve to an exhaust passage, the hunting of the control is preferably avoided by minimizing a change in the exhaust temperature or a change in the air/fuel ratio caused by the fuel supplied from the fuel supply valve to the exhaust passage.

On the other hand, the fuel supply valve for supplying fuel to the exhaust passage in the conventional exhaust heating unit disclosed in PTL 1 for example basically has the same configuration as that of a fuel injection valve for injecting fuel pressurized at a predetermined driving cycle. Thus, the hunting of the control can be effectively avoided by minimizing the driving cycle to the fuel supply valve, by minimizing the energized time per one shot, and by minimizing the amount of fuel supplied to the exhaust passage during the energized time per one shot.

However, in the case of the conventional fuel supply valve, it has been known that the reduction of the energized time per one shot causes a sudden increase of the variation of the amount of the fuel supplied to the exhaust passage. This is caused by the structure of the fuel supply valve itself and an influence by the viscosity of the fuel itself, meaning that different amounts of fuel are supplied to the exhaust passage depending on the manufacturing tolerances of the individual fuel supply valves. Due to the technical background of the fuel supply valve as described above, blindedly minimizing the energized time per one shot is essentially impossible. Thus, the energized time per one shot has been conventionally determined so that the maximum variation error of the fuel supply caused by the manufacturing tolerances of the individual fuel supply valves for example is equal to or lower than the maximum tolerance of the amount of the fuel supplied to the exhaust passage during the energized time per one shot to the fuel supply valve.

Thus, the conventional exhaust heating unit has a disadvantage as described below. That is, when the amount of fuel supplied to the exhaust passage is not so high, the driving cycle of the fuel supply valve is increased to thereby deteriorate the fuel ignitability. Furthermore, a change in the exhaust temperature or the air/fuel ratio is increased depending on when fuel is supplied and when no fuel is supplied, thus causing the hunting phenomenon of the control.

It is an objective of the present invention to provide a method for supplying fuel that can reduce the energized time per one shot to the fuel supply valve than in the case of the conventional structure.

Solution to Problem

The present invention is in a method for supplying fuel from a fuel supply valve to an exhaust passage at an upstream side of an exhaust emission purifier, the method comprises the steps of calculating, based on the status of the exhaust emission purifier, a required supply of fuel to be supplied from the fuel supply valve to the exhaust passage; reading a unit fuel supply L_(U) to be supplied to the exhaust passage in accordance with a energized time t_(U) to the fuel supply valve per one shot; intermittently supplying, with a driving cycle depending on the required supply, fuel of the unit fuel supply L_(U) from the fuel supply valve to the exhaust passage; reading the maximum tolerance E_(A) corresponding to the unit supply L_(U); reading the maximum variation error E_(DU) of the fuel supply valve corresponding to the unit supply L_(U); calculating, regard to the fuel the unit supply L_(U), an actual fuel supply g actual supplied to the exhaust passage; setting a target fuel supply L_(UT) that is less than the unit supply L_(U) by a certain amount; reading the maximum variation error E_(DT) of the fuel supply valve corresponding to the target fuel supply L_(UT); judging whether E_(DT)−E_(DU)<E_(A)−(L_(U)−g) is established or not; interpolating, when it is judged that E_(DT)−E_(DU)<E_(A)−(L_(U)−g) is established, a energized time T_(UT) to the fuel supply valve corresponding to the target fuel supply L_(UT) as a function of (L_(U)/g); and updating the target fuel supply L_(UT) as a new unit fuel supply L_(U) and using the function of (L_(U)/g) as a new energized time t_(U) to drive the fuel supply valve to supply fuel to the exhaust passage.

In the method for supplying fuel according to the present invention, the step of reading a unit fuel supply L_(U) to be supplied to the exhaust passage in accordance with a energized time t_(U) to the fuel supply valve per one shot may read the latest updated unit supply L_(U).

When fuel to be supplied from the fuel supply valve in accordance with the required supply at every driving cycle of the fuel supply valve is in an amount exceeding the double of the unit fuel supply, a half of the to-be-supplied amount may be supplied.

The state of the exhaust emission purifier for calculating the required supply is a temperature of the exhaust emission purifier or an air/fuel ratio of exhaust flowing therein, and the method may further comprise a step of judging, by carrying-out of the step of intermittently supplying fuel from the fuel supply valve to the exhaust passage for the energized time t_(U), whether the temperature of the exhaust emission purifier or the air/fuel ratio of the exhaust flowing therein is convergent or not. In this instance, only when it is judged that the temperature of the exhaust emission purifier or the air/fuel ratio of the exhaust flowing therein is convergent, the step of judging whether E_(DT)−E_(DU)<E_(A)−(L_(U)−g) is established or not may be carried out. In this case, the step of judging whether the temperature of the exhaust emission purifier or the air/fuel ratio of the exhaust flowing therein is convergent or not may include a step of judging whether at least one of the temperature of the exhaust emission purifier and the change rate thereof is within a predetermined range or not, or whether at least one of the air/fuel ratio of the exhaust flowing in the exhaust emission purifier and the change rate thereof is within a predetermined range or not.

When the sum of a detection error of the air/fuel ratio and a detection error of an air-intake amount is less than the maximum tolerance, the step of judging whether E_(DT)−E_(DU)<E_(A)−(L_(U)−g) is established or not may be carried out.

The method may further comprise a step of judging whether an amount of EC passing through the exhaust emission purifier has a value equal to or less than a predetermined value. In this instance, when it is judged that an amount of HC passing through the exhaust emission purifier has a value equal to or less than a predetermined value, the step of judging whether E_(DT)−E_(DU)<E_(A)−(L_(U)−g) is established or not may be carried out.

The method may further comprise a step of judging whether a value E_(T)/ΔT_(C) obtained by dividing a detection temperature error E_(T) of the exhaust emission purifier by the rate ΔT_(C) of temperature increase of the exhaust emission purifier per unit time smaller than the maximum tolerance E_(A) or not. In this instance, when it is judged that E_(T)/ΔT_(C)<E_(A) is established, the step of judging whether E_(DT)−E_(DU)<E_(A)−(L_(U)−g) is established or not may be carried out. In this case, the method may further comprise a step of judging whether an amount of HC passing through the exhaust emission purifier has a value equal to or less than a predetermined value. In this instance, only when it is judged that an amount of HC passing through the exhaust emission purifier has a value equal to or less than a predetermined value, the step of judging whether E_(T)/ΔT_(C)<E_(A) is established or not may be carried out.

Advantageous Effects of Invention

According to the method for supplying fuel of the present invention, a unit supply of fuel can be reduced without exceeding the maximum tolerance. This can consequently reduce the driving cycle of the fuel supply valve, thus suppressing the hunting phenomenon of the control than in the case of the conventional structure.

In order to read the unit supply L_(U) of fuel supplied to the exhaust passage, the updated latest unit supply L_(U) can be read to thereby improve the initial accuracy when the fuel supply is reduced.

when the fuel amount to be supplied from the fuel supply valve at every driving cycle of the fuel supply valve in accordance with a required supply exceeds the double of the unit fuel supply, a half of the to-be-supplied amount can be supplied to thereby suppress a sudden change in the fuel supply per one shot. This can consequently further suppress the hunting phenomenon of the control due to a change in the fuel supply. Furthermore, the main effect of the invention can be continuously obtained by continuously supplying the unit supply of fuel as long as possible.

Only when the temperature of the exhaust emission purifier or the air/fuel ratio of the exhaust flowing therein is convergent, a step is performed to determine whether E_(DT)−E_(DU)<E_(A)−(L_(U)−g) is established or not. By doing this, a control under a transitional control can be avoided. This can consequently further suppress the hunting phenomenon of the control. In particular, a control under a transitional control can be securely avoided by judging whether at least one of the temperature of the exhaust emission purifier and the change rate thereof is within a predetermined range or whether at least one of the air/fuel ratio of the exhaust flowing in the exhaust emission purifier and the change rate thereof is within a predetermined range or not.

When the sum of the detection error of the air/fuel ratio and the detection error of the air-intake amount is lower than the maximum tolerance, whether E_(DT)−E_(DU)<E_(A)−(L_(U)−g) is established or not can be judged to thereby securely maintain a reliable control.

When the HC amount passing through the exhaust emission purifier is judged to be equal to or less than a predetermined value, whether E_(DT)−E_(DU)<E_(A)−(L_(U)−g) is established or not can be judged to thereby securely maintain a reliable control.

When it is judged that the value E_(T)/ΔT_(C) obtained by dividing the detection temperature error E_(T) of the exhaust emission purifier by the rate ΔT_(C) of temperature increase of the exhaust emission purifier per unit time is lower than the maximum tolerance E_(A), whether E_(DT)−E_(DU)<E_(A)−(L_(U)−g) is established or not can be judged to thereby obtain a similar effect. In particular, only when the HC amount passing through the exhaust emission purifier is judged to be equal to or less than the predetermined value, whether E_(T)/ΔT_(C)<E_(A) or not can be judged to thereby further maintain a reliable control.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a conceptual diagram schematically illustrating a vehicle engine system including an exhaust heating unit according to the present invention;

FIG. 2 is a control block diagram illustrating the main part of the embodiment shown in FIG. 1;

FIG. 3 is a graph schematically illustrating the required supply corresponding to the driving cycle of the furl supply in the embodiment shown in FIG. 1;

FIG. 4 is a graph schematically illustrating the energized time of the fuel supply valve and the maximum tolerance thereof and the maximum variation error of the individual fuel supply valves;

FIG. 5 is a graph schematically illustrating the characteristic of an airflow meter;

FIG. 6 is a graph schematically illustrating the characteristic of an air/fuel ratio sensor;

FIG. 7 is a graph schematically illustrating the relation between the amount of HC in the exhaust and the lean shift amount of the detection value by the air/fuel ratio sensor;

FIG. 8 is a map schematically illustrating the relation between the reaction rate of the catalyst temperature and the catalyst and the HC amount in the exhaust and the O₂ concentration;

FIG. 9 is a flowchart showing, together with FIG. 10, the procedure for setting, in the embodiment shown in FIG. 1, the fuel supply from the fuel supply valve per one shot in a catalyst activation mode;

FIG. 10 is a flowchart showing, together with FIG. 9, the procedure for setting the fuel supply from the fuel supply valve per one shot in the catalyst activation mode;

FIG. 11 is a flowchart showing the details of the subroutine of the fuel addition in the flowchart shown in FIG. 9;

FIG. 12 is a flowchart showing, together with FIG. 13, the procedure for setting the fuel supply from the fuel supply valve per one shot in a catalyst regenerating mode; and

FIG. 13 is a flowchart showing, together with FIG. 12, the procedure for setting the fuel supply from the fuel supply valve per one shot in the catalyst regenerating mode.

DESCRIPTION OF EMBODIMENTS

An embodiment in which the present invention is applied to a compression ignition type internal combustion engine will be in detail explained with reference to FIG. 1 to FIG. 13. The present invention is not, however, limited to the embodiment, and the construction thereof may be freely modified corresponding to required characteristics. The present invention is effectively applied to a spark ignition type internal combustion engine in which gasoline, alcohol, LNG (Liquefied Natural Gas) or the like is used as fuel to be ignited by a spark plug, for example.

FIG. 1 schematically illustrates the main part of the engine system in this embodiment. FIG. 2 illustrates the control blocks of the main part. FIG. 1 does not illustrate a valve actuating mechanism for the intake and exhaust of the engine 10 and a throttle mechanism and a silencer as well as a general EGR apparatus as an auxiliary machine of the engine 10 for example. FIG. 1 also does not illustrate a part of various sensors required for the smooth operation of the engine 10 and the above-described auxiliary machines.

The engine 10 in this embodiment is a multicylinder internal-combustion engine in which fuel of light oil is directly injected from a fuel injection valve 11 to a combustion chamber 10 a in a compressed state to thereby cause spontaneous ignition. However, according to the characteristic of the present invention, the engine 10 also may be a single-cylinder internal-combustion engine.

A cylinder head 12 includes an intake port 12 a and an exhaust port 12 b opposed to the combustion chamber 10 a. The cylinder head 12 includes a valve actuating mechanism (not shown) including an intake valve 13 a for opening and closing the intake port 12 a and an exhaust valve 13 b for opening and closing the exhaust port 12 b. The fuel injection valve 11 opposed to the center of the upper end of the combustion chamber 10 a is also mounted on the cylinder head 12 so as to be positioned between the intake valve 13 a and the exhaust valve 13 b.

The amount and the injection timing of the fuel injected from the fuel injection valve 11 into the combustion chamber 10 a is controlled by the Electronic Control Unit (ECU) 15 based on the vehicle operating condition including the depression amount of the accelerator pedal 14 by the driver. The depression amount of the accelerator pedal 14 is detected by an accelerator opening sensor 16. The detection information is outputted to the ECU 15.

The ECUI 15 includes: an operating status determining section 15 a for determining the vehicle operating condition based on the information from this accelerator opening sensor 16 and various sensors for example (which will be described later); a fuel injection setting unit 15 b; and a fuel injection valve driving unit 15 c. The fuel injection setting unit 15 b sets, based on the determination result by the operating status determining section 15 a, the injection amount and the injection timing of fuel from the fuel injection valve 11. The fuel injection valve driving unit 15 c controls the operation of fuel injection valve 11 so that the fuel in an amount set by the fuel injection setting unit 15 b is injected from the fuel injection valve 11 at the set timing.

The cylinder block in which the piston 17 a reciprocates is mounted on a crank angle sensor 18. The crank angle sensor 18 detects the rotation phase of the crankshaft 17 c connected via a connecting rod 17 b to the piston 17 a (i.e., a crank angle) to output this to the ECU 15. The operating status determining section 15 a of the ECU 15 determines, based on the information from this crank angle sensor 18, the rotation phase of the crankshaft 17 c and the engine rotational speed as well as the vehicle speed for example on a real-time basis.

An air-intake pipe 19 connected to the cylinder head 12 so as to communicate with the intake port 12 a defines the air-intake passage 19 a together with the intake port 12 a. The exhaust pipe 20 connected to the cylinder head 12 so as to communicate with the exhaust port 12 b defines the exhaust passage 20 a together with the exhaust port 12 b.

An exhaust turbo-supercharger (hereinafter simply referred to as a supercharger) 21 is provided so as to connect the air-intake pipe 19 and the exhaust pipe 20. This supercharger 21 uses the kinetic energy of the exhaust flowing in the exhaust passage 20 a to supercharge the combustion chamber 11 a to increase the intake filling efficiency. The supercharger 21 in this embodiment is a turbocharger in which the main part is composed of a compressor 21 a and an exhaust turbine 21 b rotating with this compressor 21 a in an integrated manner. The compressor 21 a is provided on the midway of the air-intake pipe 19 positioned at the upstream of the surge tank 19 b provided on the midway of the air-intake pipe 20. The exhaust turbine 21 b is provided on the midway of the exhaust pipe 20 connected to the cylinder head 12 so as to communicate with the exhaust port 12 b. In order to reduce the intake temperature heated via the compressor 21 a by the heat transfer from the exhaust turbine 21 b subjected to a high-temperature exhaust, an intercooler 21 c is provided. This intercooler 21 c is provided on the midway of the air-intake passage 19 a between the compressor 21 a and the surge tank 19 b provided on the midway of the air-intake pipe 19.

The air-intake pipe 19 provided at the upstream of the compressor 21 a of the supercharger 21 includes an airflow meter 22 that detects the flow rate V_(A) of the intake flowing in the air-intake passage 19 a (which will be hereinafter referred to as an air-intake amount) to output this to the ECU 15.

An exhaust emission purifier 23 is provided on the midway of the exhaust pipe 20 between the exhaust turbine 21 b of the supercharger 21 and a silencer (not shown). The exhaust emission purifier 23 functions to detoxify the toxic substance generated by the combustion of mixed air in the combustion chamber 10 a. The exhaust emission purifier 23 in this embodiment includes, in an order from the upstream side, generally well-known Nitrogen Oxides (NO_(X)) storage catalytic converter 23 a, Diesel Particulate Filter (DPF) 23 b, and an oxidation catalytic converter 23 c.

An exhaust heating unit 24 is provided on the midway of the exhaust passage 20 a between the exhaust port 12 b and the exhaust turbine 21 b of the supercharger 21. This exhaust heating unit 24 functions to heat the exhaust from the engine 10 to the exhaust emission purifier 23 to activate the oxidation catalytic converter 23 c of the exhaust emission purifier 23 and to maintain the active condition or functions to subject the DPF 23 b to a regenerating processing or the NO_(X) storage catalytic converter 23 a to a deoxidation processing. The exhaust heating unit 24 in this embodiment includes a fuel supply valve 24 a and a glow plug 24.

The amount of the fuel supplied from the fuel supply valve 24 a mounted on the exhaust pipe 20 to the exhaust passage 20 a is set, based on the determination result by a fuel supply requirement determining section 15 d of the ECU 15 (which will be described later), by the fuel supply setting section 15 e of the ECU 15. The fuel supply valve driving section 15 f of the ECU 15 controls the operation of the fuel supply valve 24 a so that the fuel in an amount set by fuel supply setting section 15 e is supplied from the fuel supply valve 24 a to the exhaust passage 20 a.

The glow plug 24 b for igniting the fuel supplied from the fuel supply valve 24 a to the exhaust passage 20 a is fixed to the exhaust pipe 20 so that the heat-generating portion thereof protrudes to the exhaust passage 20 a to be opposed to an injection region of the fuel injected from the fuel supply valve 24 a. This glow plug 24 b is connected to an in-vehicle power source (not shown) via the glow plug driving section 15 g of the ECU 15. The glow plug driving section 15 g switches ON/OFF of the conduction of the glow plug 24 b based on the determination result by the fuel supply requirement determining section 15 d of the ECU 15.

The exhaust passage 20 a at the upstream side of the fuel supply valve 24 a includes a first exhaust temperature sensor 25. This first exhaust temperature sensor 25 detects the exhaust temperature T_(I) flowing in the DPF 23 b to output this to the ECU 15.

The exhaust passage 20 a between the NO_(X) storage catalytic converter 23 a and the DPF 23 b has an air/fuel ratio sensor 26. This air/fuel ratio sensor 26 detects the air/fuel ratio R_(N) of the exhaust flowing therein to output this to the ECU 15. The DPF 23 b and the oxidation catalytic converter 23 d have therebetween a catalyst temperature sensor 27 that detects the temperature T_(C) of the oxidation catalytic converter 23 c to output this to the ECU 15. The exhaust passage 20 a at the downstream side of the oxidation catalytic converter 23 c has the second exhaust temperature sensor 28 that detects the exhaust temperature T_(O) having passed through the oxidation catalytic converter 23 c to output this to the ECU 15.

The fuel supply requirement determining section 15 d of the ECU 15 determines, based on the determination result of the operation condition by the operating status determining section 15 a, the necessity of the activation of the oxidation catalytic converter 23 c and the necessities of the regenerating processing in the DPF 23 b and the NO_(X) deoxidation processing in the NO_(X) storage catalytic converter 23 a. When this fuel supply requirement determining section 15 d determines that the activation of the oxidation catalytic converter 23 c as well as the regenerating processing in the DPF 23 b and the NO_(X) deoxidation processing in the NO_(X) storage catalytic converter 23 a are required, then the addition of fuel through the fuel supply valve 24 a will be performed. The determination result by this fuel supply requirement determining section 15 d is outputted to the glow plug driving section 15 g of the ECU 15, the fuel supply setting section 15 e, and a unit fuel supply updating section 15 h (which will be described later).

The fuel supply requirement determining section 15 d of the ECU 15 determines that there is a fuel supply requirement (i.e., the exhaust heating unit 24 must be operated) when any of the following cases “a” to “d” occurs.

a: a case where the oxidation catalytic converter 23 c is inactive or is expected to be inactive. b: a case where the DPF 23 b is clogged by the deposition of HC. a case where the storage of NO_(X) by the NO_(X) storage catalytic converter 23 a is in a saturated condition. d. a case where the regenerating processing of the DPF 23 b is required even when the DPF 23 b is not clogged. The case “a” can be judged based on the temperature information T_(I), T_(O), and T_(C) from the first exhaust temperature sensor 25 and the second exhaust temperature sensor 26 as well as the catalyst temperature sensor 27. The case “b” can be judged based on the accumulated operating time of the engine 10 or the accumulated fuel injection amount from the fuel injection valve 11 for example and also can be judged by an exhaust pressure sensor. The case “c” can be similarly judged based on the accumulated operating time of the engine 10 or the accumulated fuel injection amount from the fuel injection valve 11 for example.

In order to maintain the correct performance of the exhaust emission purifier 23, the fuel supply setting section 15 e of the ECU 15 sets the fuel amount to be supplied to the exhaust passage 20 a (hereinafter referred to as a required supply) to L_(TA) and L_(TR).

More specifically, based on the exhaust temperature T_(I) and the air suction amount V_(A) per a predetermined time (e.g., 1 second), the activation required fuel supply L_(TA) to be supplied to the exhaust passage 20 a in order to maintain the active condition of the oxidation catalytic converter 23 c is set based on the following formula (1). The exhaust temperature T_(I) is the exhaust temperature that flows at the upstream side of the oxidation catalytic converter 23 c and that flows in the exhaust passage 20 a proximal to the oxidation catalytic converter 23 c. The exhaust temperature T_(I) will be hereinafter referred to as a catalyst upstream exhaust temperature. The air suction amount V_(A) per a predetermined time (which will be hereinafter referred to as an air-intake amount) is acquired from the airflow meter 22.

L _(TA)={(T _(L) −T _(I))V _(A) ·C}/J  (1)

In the formula, T_(L) means the lowest temperature at which the oxidation catalytic converter 23 c is in an active condition and is stored in the fuel supply setting section 15 e in advance. C shows the air specific heat. J shows the heat generation amount of the fuel supplied to the exhaust passage 20 a and is also stored in the fuel supply setting section 15 e in advance. The catalyst upstream exhaust temperature T_(I) is acquired from the first exhaust temperature sensor 25.

When the fuel supply requirement determining section 15 d determines that the regenerating processing by the DPF 23 b constituting the exhaust emission purifier or the NO_(X) deoxidation processing by the NO_(X) storage catalystic converter is required, then the regenerating required fuel supply L_(TR) to be supplied to the exhaust passage 20 a is set based on the following formula (2).

L _(TR) =V _(A) /R _(T))−q  (2)

In this formula, R_(T) shows the air/fuel ratio as a command of the exhaust flowing through the exhaust passage 20 a to the exhaust emission purifier 23 (hereinafter referred to as a target air/fuel ratio) and is stored in the fuel supply setting section 15 e in advance. In this formula, q shows the injection amount of the fuel injected from the fuel injection valve 11 to the combustion chamber 10 a of the engine 10 and is acquired from the fuel injection valve driving unit 15 c.

The information regarding the required fuel supplies L_(TA) and L_(TR) set by the fuel supply setting section 15 e (which will be hereinafter collectively referred to as a required fuel supply L_(T) for convenience) is outputted to the fuel supply valve driving section 15 f and the unit fuel supply updating section 15 h of the ECU 15.

The fuel supply valve driving section 15 f performs, at every calculation cycle t_(P), a processing to multiply the required fuel supply L_(T) set by the fuel supply setting section 15 e with the calculation cycle t_(P) (e.g., 20 milliseconds) to totalize the resultant values. When the fuel totalized value obtained at every calculation cycle t_(P) reaches the unit fuel supply L_(U) updated by the unit fuel supply updating section 15 h, the energized time t_(U) corresponding to this unit fuel supply L_(U) is given to the fuel supply valve 24 a. At the same time, the fuel totalized value is updated to a value obtained by (totalized value−unit supply L_(U)). Then, the fuel totalization processing is repeated to drive the fuel supply valve 24 intermittently. Therefore, the higher the required fuel supply L_(T) per a predetermined time is, the shorter the driving interval of the fuel supply valve 24 a is. The lower the required supply L_(T) per a predetermined time is, the longer the driving interval of the fuel supply valve 24 a is. The driving information from the fuel supply valve driving 15 f to the fuel supply valve 24 a is outputted to the surplus tolerance calculating section 15 i of the ECU 15.

When the engine 10 is in a transitional operating condition (e.g., in a sudden acceleration requiring the supply of a large amount of fuel within a short time), the driving cycle t_(C) of the fuel supply valve 24 a must be synchronized with the fuel burst interval of the respective cylinders of the engine 10. As a result, there may be a case where, even when the unit fuel supply L_(U) is supplied to the exhaust passage 20 a at every driving cycle t_(C) matching the fuel burst interval of the respective cylinders of the engine 10, the fuel supply ratio is insufficient to thereby fail to provide an appropriate control. In this embodiment, only when the required supply ΔL_(T) to be supplied at every driving cycle t_(C) of the fuel supply valve 24 a (=ΔL_(A)·t_(C), ΔL_(TR)·t_(C)) exceeds the double of the unit fuel supply L_(U), a half of the required fuel supply L_(T) multiplied with the driving cycle t_(C) is supplied from the fuel supply valve 24 a to the exhaust passage 20 a. FIG. 3 schematically illustrates the change of the required fuel supply ΔL_(T) to be supplied at the respective times t₁ to t₅ with the shortest driving cycle t_(C) of the fuel supply valve 24 a. In FIG. 3, the required fuel supply Δ_(T) accumulates in the period of time t₁ to time t₃ to exceed the unit fuel supply L_(U). At the time t₃ and time t₄ at which the required fuel supply L_(T) at every driving cycle t_(C) exceeds the double of the unit fuel supply L_(U), not the unit fuel supply L_(U) but fuel in an amount of ΔL_(T)/2 is supplied. Thus, after the time t₅, the required fuel supply ΔL_(T) at every driving cycle t_(C) is convergent to a value smaller than the double of the unit fuel supply L_(U). Thus, the unit fuel supply L_(U) is supplied as in the case of the time t₁ and time t₂. This can consequently suppress a delay of a control and can suppress a sudden change of the fuel supply supplied from the fuel supply valve 24 a to the exhaust passage 20 a.

The ECU 15 includes a convergence determining section 15 j in addition to the above-described operating status determining section 15 a and fuel supply valve driving section 15 f for example.

The convergence determining section 15 j determines, based on the determination result of the operating condition from the operating status determining section 15 a, whether the oxidation catalytic converter 23 c reaches, by the supply of fuel from the fuel supply valve 24 a, to the target activation temperature T_(T) and is in a stable condition or not. The convergence determining section 15 j also determines whether the air/fuel ratio R_(N) reaches, by the supply of fuel from the fuel supply valve 24 a, to the target air/fuel ratio R_(T) and is in a stable condition or not.

The convergence determining section 15 j determines that the temperature of the oxidation catalytic converter 23 c is convergent in the vicinity of the target activation temperature T_(T) and is in a stable condition when the following two conditions are satisfied. The first condition is that that the absolute value of the value obtained by deducting from the target activation temperature T_(T) the temperature of the exhaust flowing in the exhaust passage 20 a proximal to the oxidation catalytic converter 23 c at the downstream side of the oxidation catalytic converter 23 c (which will be hereinafter referred to as a catalyst downstream exhaust temperature) is lower than a positive threshold value T_(R) set in advance. The second condition is that the absolute value of a rate dT_(O) of change in the exhaust temperature T_(O) is smaller than the threshold value dT_(R) set in advance (which is generally has a positive value close to 0). As a result, it can be securely judged that the engine 10 does not have a transitional operating condition. However, another configuration also may be used where the oxidation catalytic converter 23 c has a temperature convergent to the neighborhood of the target activation temperature T_(T) only when any of the conditions is satisfied.

Similarly, the convergence determining section 15 j determines that the exhaust flowing in the exhaust passage 20 a has the air/fuel ratio R_(N) that is convergent ant stable at the neighborhood of the target air/fuel ratio R_(T) when the following two conditions are satisfied. The first condition is that the absolute value of the value obtained by deducting, from the target air/fuel ratio R_(T), the air/fuel ratio R_(N) acquired by the air/fuel ratio sensor 26 is smaller than the positive threshold value dR_(R) set in advance. The second condition is that the rate dR_(N) of change of the air/fuel ratio R_(N) has an absolute value smaller than the positive threshold value dR_(R) set in advance (which is generally has a positive value close to 0). As a result, it can be securely judged that the engine 10 does not have a transitional operating condition. However, another configuration also may be used where the exhaust flowing in the exhaust passage 20 a has the air/fuel ratio R_(N) that is convergent in the vicinity of the target air/fuel ratio R_(T) only when any of the conditions is satisfied.

By the determination processing by the convergence determining section 15 j as described above, it is possible to confirm that the engine 10 is not in a transitional operating condition. Thus, the exhaust heating unit 24 can be subjected to a smooth control. This determination result is outputted to the surplus tolerance calculating section 15 j.

FIG. 4 schematically illustrates the relation among the unit fuel supply L_(U) and the maximum tolerance E_(A) as well as the maximum variation error E_(D). It is noted that values are not positive or negative values around 0 as a center but are conveniently represented as absolute values on the basis of percentage. The maximum tolerance E_(A) shows, with regard to the unit fuel supply L_(U) set by the unit fuel supply updating section 15 h, a target control (e.g., a dislocation value for which a temperature increase control of the oxidation catalytic converter 23 c or the air/fuel ratio control of the exhaust can be convergent). The maximum tolerance E_(A) can be represented as a value equal to or less than the unit supply L_(U). Thus, the maximum tolerance E_(A) represented by percentage can be basically represented as a fixed value regardless of the magnitude of the unit supply L_(U). On the other hand, the maximum variation error E_(D) of the fuel supply, which is caused by the mechanical characteristic of the fuel supply valve 24 a itself or the viscosity of the fuel itself for example, tends to rapidly increase as shown by the solid line of FIG. 4 with the decrease of the unit fuel supply L_(U). Thus, when the unit fuel supply L_(U) is tried to be less than the unit fuel supply at which the maximum tolerance E_(A) is equal to the maximum variation error E_(D) (this unit fuel supply will be hereinafter referred to as a reference unit fuel supply L_(UC)), the maximum variation error E_(D) must be considered. Theerfore, the maximum tolerance E_(A) must be further estimated to be smaller in consideration of the difference between the maximum variation error E_(D) and the maximum tolerance E_(A) so that the unit fuel supply L_(U) has an error that is smaller than (E_(A)−E_(D)).

The surplus tolerance calculating section 15 i stores therein the map as show in FIG. 4. The surplus tolerance calculating section 15 i deducts, from the totalized value ΣL_(D) of the unit fuel supply L_(U) set by the unit fuel supply updating section 15 h, the fuel supply to be actually supplied to correspond to the totalized value ΣL_(U) (hereinafter referred to as an actual fuel supply) to calculate the supply error E_(U). Then, the surplus tolerance calculating section 15 i deducts the calculated supply error E_(U) from the maximum tolerance E_(A) corresponding to the current unit supply L_(U) stored in the map of FIG. 4 to calculate the amount ΔE_(A) of the surplus tolerance. The totalized value ΣL_(U) is an instruction value of the amount of the fuel that is driven, during the detection period of the intake amount V_(A), by an instruction from the fuel supply valve driving section 15 f and that is supplied from the fuel supply valve 24 a to the exhaust passage 20 a. Thus, the supply error E_(U) can be represented by (Σ_(U)−g). The actual fuel supply g is calculated based on the following formula.

g=(ΔT _(I) ·V _(A) ·C)  (3)

In the formula, ΔT_(I) shows a difference between T_(I) detected by the first exhaust temperature sensor 25 and the exhaust temperature T_(O) detected by the second exhaust temperature sensor 28 and is represented by ΔT_(I)=T_(O)−T_(I). Thus, the amount ΔE_(A) of the surplus tolerance is represented as shown by the following formula (4).

ΔE _(A) =E _(A) −ΣL _(U)+(ΔT _(I) ·V _(A) ·C/J)  (4)

The amount ΔE_(A) of the surplus tolerance calculated by the surplus tolerance calculating section 15 i is outputted to the unit fuel supply updating section 15 h.

The unit fuel supply updating section 15 h in this embodiment updates the fuel supply per one energized time t_(U) supplied from the fuel supply valve 24 a to the exhaust passage 20 a (i.e., the unit fuel supply L_(U)) and outputs the updated unit fuel supply L_(U) to the fuel supply valve driving section 15 f. In this embodiment, the initial value L_(US) of the unit fuel supply L_(U) is stored in advance in the unit fuel supply updating section 15 h. Thus, such a control is carried out that stepwisedly reduces the unit fuel supply L_(U) from this initial value L_(US) by a certain amount of the target unit fuel supply L_(UT). Basically, the unit fuel supply L_(U) is updated to have a smaller value so that, with regard to the required fuel supply L_(T) set by the fuel supply setting section 15 e, the unit fuel supply L_(U) is supplied with the shortest addition interval (the driving cycle t_(C) of the fuel supply valve 24 a) as possible. In this case, the initial value L_(US) of the unit fuel supply is set to a value sufficiently higher than the reference unit fuel supply L_(UC). The target unit fuel supply L_(UT) is set to a value smaller than the current unit fuel supply L_(U) by a predetermined amount and is updated to have a smaller value, when possible, by the update processing.

More particularly, fuel of the target unit fuel supply L_(UT) smaller than the current unit fuel supply L_(U) by a certain amount is set. A different processing is performed depending on the case where the target unit fuel supply L_(UT) is higher than the reference unit fuel supply L_(UC) and the case where the target unit fuel supply L_(UT) is lower than the reference unit fuel supply L_(UC). Specifically, when the target unit fuel supply L_(UT) is higher than the reference unit fuel supply L_(UC), there is no need to consider the maximum variation error E_(D). Thus, when the supply error E_(U) calculated by the surplus tolerance calculating section 15 i is lower than the maximum tolerance E_(A), the target unit fuel supply L_(UT) is updates as a new unit fuel supply L_(U).

When the target unit fuel supply L_(UT) is lower than the reference unit fuel supply L_(UC), then the target unit fuel supply L_(UT) is set to have a value smaller than the current unit fuel supply L_(U) by a certain amount. The maximum variation error E_(DT) of the target unit fuel supply L_(UT) and the maximum variation error E_(DU) of the current unit fuel supply L_(U) are read out from the map of FIG. 4. Then, the amount ΔE_(D) of the surplus variation error obtained by deducting from the maximum variation error E_(DT) corresponding to the target unit fuel supply L_(UT) the maximum variation error E_(DU) corresponding to the current unit fuel supply L_(U) (=E_(DT)−E_(DU)) is compared with the amount ΔE_(A) of the surplus tolerance given from the surplus tolerance calculating section 15 i. Then, when it is judged that the amount ΔE_(A) of the surplus tolerance is lower than the amount ΔE_(D) of the surplus variation error, the target unit fuel supply L_(UT) is updated as a new unit fuel supply L_(U).

In any of the cases, the energized time t_(U) corresponding to the updated unit fuel supply L_(U) is interpolated as shown in the following formula (5).

t _(U) =t _(UT) >k(ΣL _(U) /g)  (5)

The energized time t_(U) corresponding to the updated unit fuel supply L_(U) also can be interpolated by any appropriate function formula other than the formula (5) including (ΣL_(U)/g) as a variable. For example, the following formula (6) also can be used.

t _(U) =t _(UT)+(ΣL _(U) /g)  (6)

Furthermore, it is also effective to multiply (ΣL_(U)/a) in order to suppress a sudden change of the right sides of the formulae (5) and (6), with such an interpolation coefficient that is higher than 0 and that is equal to 0 and that is equal to or lower than 1. By including such an interpolation coefficient in the formulae (5) and (6), it is possible to avoid an adverse influence by an error of sensors for example used to calculate the unit fuel supply L_(U) and the actual fuel supply g or the calculation of the energized time t_(U) during a transitional operating condition of the vehicle. This interpolation coefficient can be set in advance based on the magnitude of the error based on the resolution of the sensors for example or the vehicle transitional operating condition for example.

As described above, based on the actual fuel supply g corresponding to the unit fuel supply L_(U), the energized time t_(UT) corresponding to the target unit fuel supply L_(UT) is interpolated. By doing this, even when the current unit fuel supply L_(U) is reduced to the target unit fuel supply L_(UT), the resultant error can be equal to or lower than the maximum tolerance E_(A). Thus, when the amount ΔE_(A) of the surplus tolerance exceeds the amount ΔE_(D) of the surplus variation error and the current unit fuel supply L_(U) is reduced to the target unit fuel supply L_(UT) this exceeds the maximum tolerance E_(A). Thus, no update of the unit fuel supply L_(U) is performed.

As described above, the smaller the unit fuel supply L_(U) is when compared with the required fuel supply L_(T), fuel is supplied from the fuel supply valve 24 a to the exhaust passage 20 a with a shorter driving cycle t_(C). As a result, fuel supplied to the exhaust passage 20 a shows a smaller temporal fluctuation range, thus providing a smaller fluctuation range of the air/fuel ratio R_(N) in the exhaust in particular.

The unit fuel supply updating section 15 h in this embodiment includes an update availability determining section 151 to determine the availability of the above-described update processing of the unit fuel supply L_(U) and the energized time t_(U). When this update availability determining section 151 determines that the following conditions (A) (C) (E), and (B) or (D) are satisfied, this update availability determining section 151 allows the update of the unit fuel supply L_(U) and the energized time t_(U) by the unit fuel supply updating section 15 h. When this update availability determining section 151 determines that the following conditions (A), (C), (E), and (B) or (D) are not satisfied on the other hand, this update availability determining section 151 does not allow the update of the unit fuel supply L_(U) and the energized time t_(U) by the unit fuel supply updating section 15 h. Then, unit fuel supply updating section 15 h stores the current unit fuel supply L_(U) and energized time t_(U) as the latest unit fuel supply L_(U) and energized time t_(U).

ΔE _(A) >ΔE _(D)  (A)

E _(A) >E _(VA) +E _(RT)  (B)

E _(A)>(E _(T) /E _(TC))  (C)

E _(A) >E _(U)  (E)

With regard to (A), when the amount ΔE_(A) of the surplus tolerance exceeds the amount ΔE_(D) of the surplus variation error as described above, the unit fuel supply L_(U) is not updated because the current unit fuel supply L_(U) reduced to the target unit fuel supply L_(UT) in this case exceeds the maximum tolerance E_(AT).

With regard to (B), it has been well-known that the airflow meter 22 and the air/fuel ratio sensor 26 have a unique measurement error due to the detection system thereof. FIG. 5 shows the relation between the air-intake amount by the airflow meter 22 and the measurement error. FIG. 6 shows the relation between the air/fuel ratio R_(N) by the air/fuel ratio sensor 26 and the measurement error. When the regenerating required fuel supply L_(TR) is calculated based on the above formula (2), the air-intake amount V_(A) detected by the airflow meter 22 and the air/fuel ratio R_(N) of the exhaust detected by the air/fuel ratio sensor 26 include the measurement errors E_(VA) and E_(RT) as shown in FIG. 5 and FIG. 6, respectively. As a result, some combination of the measurement errors E_(VA) and E_(RT) may exceed the maximum tolerance E_(A) for the regenerating required fuel supply L_(TR). To solve this, in this embodiment, the air/fuel ratio R_(N) of the exhaust is controlled so that, when the sum (%) of the measurement errors E_(VA) and E_(RT) of by the airflow meter 22 and the air/fuel ratio sensor 26 exceeds the maximum tolerance E_(A), the above target unit fuel supply L_(UT) is not updated as a new unit fuel supply L_(U). The above formula (5) is not also calculated.

With regard to (C), it has been known that the detection value R_(N) of the air/fuel ratio sensor 26 is dislocated to the lean side in proportion to the HC amount included in the exhaust (so-called lean shift). Thus, the error of the detection value R_(N) by the air/fuel ratio sensor due to this lean shift amount ΔE_(S) must be lower than the maximum tolerance E_(A) of the unit fuel supply L_(U). Thus, when the lean shift amount ΔE_(S) is too large, the above target unit fuel supply L_(UT) is not updated as a new unit fuel supply L_(U). Similarly, the calculation of the above formula (5) also must not be performed. In this embodiment, when the value ω·g obtained by multiplying the HC purification rate ω by the exhaust emission purifier 23 with the actual fuel supply g is lower than the lean shift amount ΔE_(S), then the above target unit fuel supply L_(UT) is updated as a new unit fuel supply L_(U) and the above formula (5) is calculated. When the value ω·g obtained by multiplying the HC purification rate ω by the exhaust emission purifier 23 with the actual fuel supply g is equal to or larger than the lean shift amount ΔE_(S) on the other hand, the above target unit fuel supply L_(UT) is not updated as a new unit fuel supply L_(U) and the above formula (5) is not performed.

FIG. 7 schematically illustrates the relation between the HC amount included in the exhaust passing through the exhaust passage 20 a including the air/fuel ratio sensor 26 and the lean shift amount ΔE_(S) in the air/fuel ratio sensor 26. The operating status determining section 15 a of the ECU 15 stores therein the map as shown in FIG. 7 in advance. The HC amount included in the exhaust is calculated by the fuel supply valve update availability determining section 151 based on the air-intake amount V_(A) and, the fuel injection amount from the fuel injection valve 11, and the fuel supply from the fuel supply valve 24 a. The HC purification rate u by the exhaust emission purifier 23 can be calculated by dividing the HC reaction rate v by the exhaust emission purifier 23 by the exhaust flow rate (which is the air-intake amount V_(A) in this case). The reaction rate v in the exhaust emission purifier 23 can be calculated based on the relation among the HC amount and O₂ concentration in the exhaust and the catalyst temperature. FIG. 8 illustrates the relation among the HC amount and O₂ concentration in the exhaust and the catalyst temperature as described above. The fuel supply valve update availability determining section 151 stores therein the map as shown in FIG. 8. The fuel supply valve update availability determining section 151 reads the reaction rate V based on the catalyst temperature T_(C) and the HC amount and O₂ concentration in the exhaust. Next, the air-intake amount V_(A) by the airflow meter 22 is divided by information to calculate the HC purification rate ω. Then, the HC purification rate ω is multiplied with the actual fuel supply g calculated based on the above formula (3) and the result is compared with the above lean shift amount ΔE_(S). Then, only when ΔE_(S)>(v/V_(A))·g is established, the unit fuel supply updating section 15 h updates the unit fuel supply L_(U) and the energized time t_(U).

With regard to (D), when a control is carried out based on the activation required fuel supply L_(TA), an influence by the detection error of the catalyst temperature sensor 27 must be avoided. Thus, it is judged whether the value (E_(T)/ΔT_(C)) obtained by dividing the detection temperature error of the exhaust emission purifier 23 (i.e., the detection error E_(T) of the catalyst temperature T_(C) detected by the catalyst temperature sensor 27) by the rate ΔT_(C) of temperature increase of the exhaust emission purifier 23 per unit time is smaller than the maximum tolerance E_(A) or not. When E_(A)>(E_(T)/ΔT_(C)) is established. Then, the unit supply L_(U) and the energized time t_(U) are updated.

With regard to (E), when the target unit fuel supply L_(UT) is more than the reference unit fuel supply L_(UC) and the supply error E_(U) is larger than the maximum tolerance E_(A), the target unit fuel supply L_(UT) cannot be updated as a new unit fuel supply L_(U).

FIG. 9 to FIG. 11 illustrate the flow of the fuel supply control in this embodiment in the catalyst activation mode to maintain the oxidation catalytic converter 23 c as described above in an activated state. First, the step S11 determines whether there is a fuel supply request or not. When it is judged that there is a fuel supply request (i.e., when it is judged that the activation of the oxidation catalytic converter 23 c in the exhaust emission purifier 23 is required), the processing proceeds to the step S12 to calculate the activation required fuel supply L_(TA). Next, the step S13 acquires the unit fuel supply L_(U) from the unit fuel supply updating section 15 h of the ECU 15. Then, the step S14 drives the fuel supply valve 24 a to start supplying fuel to the exhaust passage 20 a.

FIG. 11 illustrates the subroutine of the fuel supply. Specifically, the step S141 determines whether the required fuel supply ΔL_(TA) per unit time is less than double of the unit fuel supply L_(U) or not. When the required fuel supply ΔL_(TA) per unit time is less than double of the unit fuel supply L_(U) (i.e., there is no particular problem when fuel is continuously supplied in the unit fuel supply L_(U)), the processing proceeds to the step S142 to supply fuel with the unit fuel supply L_(U). Next, the step S143 determines whether a fuel supply flag is set or not. At an initial stage, no fuel supply flag is set. Thus, the processing proceeds to the step S144 to set a fuel supply flag. Then, the step S145 determines whether there is a fuel supply request or not. When it is judged that there is a fuel supply request (i.e., there is still a need to activate the oxidation catalytic converter 23 _(C) in the exhaust emission purifier 23), then the processing returns to the main flow of FIG. 10 to carry out the step S15 (which will be described later). When the step S145 determines that there is no fuel supply request (i.e., there is no need to activate the oxidation catalytic converter 23 _(C) in the exhaust emission purifier 23), the processing returns to the main flow of FIG. 9 to carry out the step S30 (which will be described later).

On the other hand, when the step S141 determines that the required fuel supply ΔL_(TA) per unit time exceeds the double of the unit fuel supply L_(U) (i.e., when it is judged that the continued supply of fuel in the unit fuel supply L_(U) causes an insufficient fuel supply), the processing proceeds to the step S146. Then, fuel in the amount of a half of the required fuel supply ΔL_(TA) per unit time is supplied through the fuel supply valve 24 a to the exhaust passage 20 a. Then, steps after the above step S143 are carried out.

The step S15 determines whether the new target unit fuel supply L_(UT) set to the current unit fuel supply L_(U) is less than the reference unit fuel supply L_(UC) or not. At an initial stage, the newly-set target unit fuel supply L_(UT) is equal to or more than the reference unit fuel supply L_(UC). Thus, the processing proceeds to the step S16 to allow the surplus tolerance calculating section 15 i to calculate the supply error E_(U). Next, the step S17 determines whether the supply error E_(U) is smaller than the maximum tolerance E_(A) or not. When it is judged that the supply error E_(U) is smaller than the maximum tolerance E_(A) (i.e., when it is judged that the unit fuel supply L_(U) can be updated), the processing proceeds to the step S18. Then, the set target unit fuel supply L_(UT) is updated as a new unit fuel supply L_(U) and the energized time t_(U) to the corresponding fuel supply valve 24 a is interpolated as shown in the formula (5). Then, the processing again returns to the step S11. When the step S17 determines that the supply error E_(U) is equal to or larger than the maximum tolerance E_(A) (i.e., it is judged that the unit fuel supply L_(U) cannot be updated), the current unit fuel supply L_(U) and the energized time t_(U) are directly maintained. Then, the processing again returns to the step S11.

When the above step S15 determines that the target unit fuel supply L_(UT) newly set to the current unit fuel supply L_(U) is less than the reference unit fuel supply L_(UC), (i.e., when it is judged that the maximum variation error E_(D) must be considered), then the processing proceeds to the step S19. Then, it is judged whether the absolute value of the value obtained by deducting the current catalyst downstream exhaust temperature T_(O) from the target activation temperature T_(T) of the oxidation catalytic converter 23 c is smaller than the threshold value T_(R) or not. When it is judged that the absolute value of the value obtained by deducting the current catalyst downstream exhaust temperature T_(O) from the target activation temperature T_(T) of the oxidation catalytic converter 23 c is less than the threshold value T_(R) (i.e., when it is judged that the oxidation catalytic converter 23 _(C) reaches the activation temperature), then the processing proceeds to the step S20. Then, it is judged whether the rate dT_(O) of exhaust temperature change in downstream of the catalyst is less than the threshold value dT_(R) or not. When the rate dT_(O) of exhaust temperature change in downstream of the catalyst is smaller than the threshold value dT_(R) (i.e., when the oxidation catalytic converter 23 _(C) has a temperature that is converged and stable at the activation temperature), then the processing proceeds to the step S21. Then, the supply error E_(U) is calculated. The step S22 calculates the amount ΔE_(A) of the surplus tolerance. The step S23 calculates the amount ΔE_(D) of the surplus variation error.

When the above step S19 determines that the absolute value of the value obtained by deducting the current catalyst downstream exhaust temperature T_(O) from the target activation temperature T_(T) is equal to or larger than the threshold value T_(R) (i.e., when it is judged that the oxidation catalytic converter 23 c is converged at the activation temperature), then the processing returns to the step S11. in this case, it is noted that the current unit fuel supply L_(U) and energized time t_(U) are maintained continuously. Similarly, when the step S20 determines that the exhaust temperature change rate dT_(CO) is equal to or more than the threshold value dT_(R) (i.e., when the oxidation catalytic converter 23 c is not converged at the activation temperature), the processing returns to the step S11 while maintaining the current unit fuel supply L_(U) and energized time t_(U).

After the step S23, the step S24 determines whether the amount ΔE_(A) of the surplus tolerance is more than the amount ΔE_(D) of the surplus variation error or not. When it is judged that the amount ΔE_(A) of the surplus tolerance is larger than the amount ΔE_(D) of the surplus variation error (i.e., it is judged that the unit fuel supply L_(U) can be updated to a reduced amount), the processing proceeds to the step S29. Then, it is judged whether the value (E_(T)/ΔT_(U)) obtained by dividing the detection error E_(T) of the catalyst temperature T_(C) by the rate ΔT_(C) of temperature increase of the exhaust emission purifier 23 per unit time is less than the maximum tolerance E_(A) or not. When it is judged that the value of (E_(T)/ΔT_(C)) is smaller than the maximum tolerance E_(A) (i.e., when it is judged that the unit fuel supply L_(U) can be updated to a reduced amount), the processing proceeds to the step S18. When it is judged that the value of (E_(T)/T_(C)) is equal to or larger than the maximum tolerance E_(A) (i.e., when it is judged that the unit fuel supply L_(U) cannot be updated to a reduced amount), the current unit fuel supply L_(U) and energized time t_(U) are directly maintained and the processing returns to the step S11. Similarly, when the step S24 determines that amount ΔE_(A) of the surplus tolerance is equal to or less than the amount ΔE_(D) of the surplus variation error (i.e., when it is judged that an updated unit fuel supply L_(U) deviates from the maximum tolerance E_(A)), then the current unit fuel supply L_(U) and energized time t_(U) are maintained. Then, the processing returns to the step S11.

On the other hand, when the above step S11 determines that there is no fuel supply request (i.e., it is judged that there is no need to activate the oxidation catalytic converter 23 in the exhaust emission purifier 23), then the processing proceeds to the step S30 to determine whether a fuel supply flag is set or not. When it is judged that the fuel supply flag is set, (i.e., when it is judged that the fuel supply from the fuel supply valve 24 a to the exhaust passage 20 a continued), then the processing proceeds to the step S31 to stop the fuel supply processing. Then, the step S32 resets the fuel supply flag to thereby complete a series of controls. When the above step S30 determines that no fuel supply flag is set (i.e., when it is judged that the processing to supply fuel from the fuel supply valve 24 a to the exhaust passage 20 a is not performed), the processing is completed without doing anything.

As described above, when the amount ΔE of the surplus tolerance is less than the amount ΔE_(D) of the surplus variation error, the unit fuel supply L_(U) is updated to a smaller target unit fuel supply L_(UT). As a result, the oxidation catalytic converter 23 c can have a narrower temperature amplitude to reduce the wasteful fuel supply, thus improving fuel consumption. At the same time, even the reduced unit fuel supply L_(U) can be always less than the maximum tolerance, thus securely maintaining a desired control accuracy.

In the above-described embodiment, the temperature of the oxidation catalytic converter 23 c was controlled. However, a similar control configuration also can be used when the air/fuel ratio of the exhaust is controlled.

FIG. 12 and FIG. 13 show the flow of the fuel supply control in this embodiment in the catalyst regenerating mode for performing the regenerating processing by the DPF 23 b and the deoxidation processing by the NO_(X) storage catalytic converter 23 a constituting the exhaust emission purifier 23 as described above. The steps S41 to S48, S51 to S54, and S60 to S62 in this embodiment are basically the same as the steps S11 to S18, S21 to S24, and S30 to S32 in the above flowcharts shown in FIG. 9 and FIG. 10. However, the regenerating required fuel supply L_(TR) in the step S42 is calculated by the formula (2). The fuel supply subroutine of S44 has the same procedure as that of the above embodiment shown in FIG. 11.

When the step S45 determines that the target unit fuel supply L_(UT) newly set to the current unit fuel supply L_(U) is less than the reference unit supply L_(UC) (i.e., when it is judged that the maximum variation error E_(D) must be considered), the processing proceeds to the step S49. Then, it is judged whether the absolute value of the value obtained by deducting the air/fuel ratio value R_(N) from the target air/fuel ratio value R_(T) is smaller than the positive threshold value R_(R) set in advance or not. When it is judged that the absolute value of the value obtained by deducting the air/fuel ratio value R_(N) from the target air/fuel ratio value R_(T) is less than the positive threshold value R_(R) set in advance (i.e., when it is judged that the current air/fuel ratio R_(N) substantially reaches the target air/fuel ratio R_(T)). Then, the processing proceeds to the step S50. Then, it is judged whether the rate dR_(N) of change of air/fuel ratio detected by the air/fuel ratio sensor 26 has an absolute value that is less than the threshold value dR_(R) or not. When it is judged that the rate dR_(N) of change of the air/fuel ratio R_(N) has an absolute value smaller than the threshold value dR_(R) (i.e., when it is judged that the exhaust flowing in the exhaust passage 20 a has the air/fuel ratio R_(N) that is converged and stable at the target air/fuel ratio R_(T)), the processing proceeds to the step S51 to calculate the amount ΔE_(A) of the surplus tolerance.

When the step S49 determines that the absolute value of the value obtained by deducting the current air/fuel ratio value R_(N) from the target air/fuel ratio value R_(T) is equal to or larger than the threshold value R_(R)(i.e., when it is judged that the current air/fuel ratio R_(N) is not converged at the target air/fuel ratio R_(T)), then the processing returns to the step S41. In this case, it is noted that the current unit fuel supply L_(U) and the energized time t_(U) are maintained. When the step S50 determines that the absolute value of the rate dR_(N) of change of the air/fuel ratio is equal to or more than the threshold value R_(R) (i.e., when it is judged that the exhaust flowing in the exhaust passage 20 a has the air/fuel ratio R_(N) that does not reach the target air/fuel ratio R_(T) and is unstable), the processing also returns to the step S41. In this case, the current unit fuel supply L_(U) and the energized time t_(U) are similarly maintained.

After the step S53, the step S54 determines whether amount ΔE_(A) of the surplus tolerance is more than the amount ΔE_(D) of the surplus variation error or not. When the amount ΔE_(A) of the surplus tolerance is larger than the amount ΔE_(D) of the surplus variation error, (i.e., when it is judged that the unit fuel supply L_(U) can be updated and reduced), then the processing proceeds to the step S55. Then, it is judged whether the sum of the measurement errors E_(VA) and E_(RT) of the airflow meter 22 and the air/fuel ratio sensor 26 is less than the maximum tolerance E_(A) or not. When it is judged that the sum of the measurement errors E_(VA) and E_(RT) of the airflow meter 22 and the air/fuel ratio sensor 26 is smaller than the maximum tolerance E_(A), (i.e., when it is judged that the unit fuel supply L_(U) can be updated and reduced), the processing proceeds to the step S56. Then, the HC amount in the exhaust is calculated. The step S57 calculates the lean shift amount ΔE_(S) in the air/fuel ratio sensor 26. The step S58 calculates the catalyst purification rate ω. When the step S55 determines that the sum of the measurement errors E_(VA) and E_(RT) is less than the maximum tolerance E_(A), (i.e., when it is judged that the unit fuel supply L_(U) cannot be updated and reduced), then the processing returns to the step S41 while maintaining the current unit fuel supply L_(U) and energized time t_(U).

After the step S58, the step S59 determines whether the above lean shift amount ΔE_(S) is less than a value obtained by multiplying the HC purification rate ω with the actual fuel supply g or not. When it is judged that the above lean shift amount ΔE_(S) is less than a value obtained by multiplying the HC purification rate ω with the actual fuel supply g, the processing proceeds to the step S48. When it is judged that the above lean shift amount ΔE_(S) is equal to or larger than a value obtained by multiplying the HC purification rate ω with the actual fuel supply g (i.e., when it is judged that the unit fuel supply L_(U) cannot be updated and reduced), then the processing returns to the step S41 while maintaining the current unit fuel supply L_(U) and energized time t_(U).

As described above, similarly in this embodiment, when the amount ΔE of the surplus tolerance is less than the amount ΔE_(D) of the surplus variation error, the unit fuel supply L_(U) is updated to a smaller target unit fuel supply L_(UT). As a result, the oxidation catalytic converter 23 c can have a narrower temperature amplitude to reduce the wasteful fuel supply, thus improving fuel consumption. At the same time, even the reduced unit fuel supply L_(U) can be always less than the maximum tolerance, thus securely maintaining a desired control accuracy.

It should be noted that, the present invention should be interpreted based only upon the matters described in claims, and in the aforementioned embodiments, all changes and modifications included within the spirit of the present invention can be made other than the described matters. That is, all the matters in the described embodiments are made not to limit the present invention, but can be arbitrarily changed according to the application, the object and the like, including every construction having no direct relation to the present invention.

REFERENCE SIGNS LIST

-   -   dT_(O) Rate of exhaust temperature change     -   dT_(R) Threshold value     -   dR_(N) Rate of change of air/fuel ratio     -   dR_(R) Threshold value     -   ΔE_(A) Surplus amount of tolerance     -   ΔE_(D) Surplus amount of variation error     -   ΔE_(S) Lean shift amount in air/fuel ratio sensor     -   ΔL_(T) Required supply to be supplied at every driving cycle of         fuel supply valve     -   ΔT_(C) Rate of temperature increase of exhaust emission purifier         per unit time     -   E_(A) Maximum tolerance in unit fuel supply     -   E_(D) Maximum variation error in unit fuel supply     -   E_(U) Supply error     -   E_(RT) Measurement error by air/fuel ratio sensor     -   E_(T) Measurement error by catalyst temperature sensor     -   E_(VA) Measurement error by airflow meter     -   g Actual fuel supply     -   L_(TA) Activation required fuel supply     -   L_(TR) Regenerating required fuel supply     -   L_(T) Required fuel supply     -   L_(U) Unit fuel supply     -   L_(UC) Reference unit fuel supply     -   L_(US) Initial value of unit fuel supply     -   L_(UT) Target unit fuel supply     -   R_(N) Air/Fuel ratio in exhaust     -   R_(T) Target air/fuel ratio     -   R_(R) Threshold value     -   t_(C) Driving cycle of fuel supply valve     -   t₁ to t₅ Time     -   T_(C) Temperature of oxidation catalytic converter     -   T_(O) Exhaust temperature at downstream of catalystff     -   T_(T) Target activation temperature     -   T_(R) Threshold value     -   v HC Reaction rate in exhaust emission purifier     -   V_(A) Air-intake amount     -   ω HC Purification rate by exhaust emission purifier     -   10 Engine     -   10 a Combustion chamber     -   11 Fuel injection valve     -   12 Cylinder head     -   12 a Intake port     -   12 b Exhaust port     -   13 a intake valve     -   13 b Exhaust valve     -   14 Accelerator pedal     -   15 ECU     -   15 a Operating status determining section     -   15 b Fuel injection setting section     -   15 c Fuel injection valve driving section     -   15 d Fuel supply requirement determining section     -   15 e Fuel supply setting section     -   15 f Fuel supply valve driving section     -   15 g Glow plug driving section     -   15 h Unit fuel supply updating section     -   15 i Surplus tolerance calculating section     -   15 j Convergence determining section     -   15 l Update availability determining section     -   16 Accelerator opening sensor     -   17 Cylinder block     -   17 a Piston     -   17 b Connecting rod     -   17 c Crankshaft     -   18 Crank angle sensor     -   19 Air-intake pipe     -   19 a Air-intake passage     -   19 b Surge tank     -   20 Exhaust pipe     -   20 a Exhaust passage     -   21 Supercharger (Turbocharger)     -   21 a Compressor     -   21 b Exhaust turbine     -   21 c intercooler     -   22 Airflow meter     -   23 Exhaust emission purifier     -   23 a NO_(X) Storage catalytic converter     -   23 b DPF     -   23 c Oxidation catalytic converter     -   24 Exhaust heating unit     -   24 a Fuel supply valve     -   24 b Glow plug     -   25 First exhaust temperature detecting sensor     -   26 Air/Fuel ratio detecting sonsor     -   27 Catalytic converter temperature detecting sensor     -   28 Second exhaust temperature detecting sensor 

1-9. (canceled)
 10. A method for supplying fuel from a fuel supply valve to an exhaust passage at an upstream side of an exhaust emission purifier, the method comprising the steps of: calculating, based on the status of the exhaust emission purifier, a required supply of fuel to be supplied from the fuel supply valve to the exhaust passage; reading a unit fuel supply L_(U) to be supplied to the exhaust passage in accordance with a energized time t_(U) to the fuel supply valve per one shot; intermittently supplying, with a driving cycle depending on the required supply, fuel of the unit fuel supply L_(U) from the fuel supply valve to the exhaust passage; reading the maximum tolerance E_(A) corresponding to the unit supply L_(U); reading the maximum variation error E_(DU) of the fuel supply valve corresponding to the unit supply L_(U); calculating, regard to the fuel the unit supply L_(U), an actual fuel supply g actually supplied to the exhaust passage; setting a target fuel supply L_(UT) that is less than the unit supply L_(U) by a certain amount; reading the maximum variation error E_(DT) of the fuel supply valve corresponding to the target fuel supply L_(UT); judging whether E_(DT)−E_(DU)<E_(A)−(L_(U)−g) is established or not; interpolating, when it is judged that E_(DT)−E_(DU)<E_(A)−(L_(U)−g) is established, an energized time T_(UT) to the fuel supply valve corresponding to the target fuel supply L_(UT) as a function of (L_(U)/g); and updating the target fuel supply L_(UT) as a new unit fuel supply L_(U) and using the function of (L_(U)/g) as a new energized time t_(U) to drive the fuel supply valve to supply fuel to the exhaust passage.
 11. The method as claimed in claim 10, wherein: the step of reading a unit fuel supply L_(U) to be supplied to the exhaust passage in accordance with an energized time t_(U) to the fuel supply valve per one shot reads the latest updated unit supply L_(U).
 12. The method as claimed in claim 10, wherein when fuel to be supplied from the fuel supply valve in accordance with the required supply at every driving cycle of the fuel supply valve is in an amount exceeding the double of the unit fuel supply, a half of the to-be-supplied amount is supplied.
 13. The method as claimed in claim 11, wherein when fuel to be supplied from the fuel supply valve in accordance with the required supply at every driving cycle of the fuel supply valve is in an amount exceeding the double of the unit fuel supply, a half of the to-be-supplied amount is supplied.
 14. The method as claimed in claim 10, wherein the state of the exhaust emission purifier for calculating the required supply is a temperature of the exhaust emission purifier or an air/fuel ratio of exhaust flowing therein, and the method further comprises a step of judging, by carrying-out of the step of intermittently supplying fuel from the fuel supply valve to the exhaust passage for the energized time t_(U), whether the temperature of the exhaust emission purifier or the air/fuel ratio of the exhaust flowing therein is convergent or not and, only when it is judged that the temperature of the exhaust emission purifier or the air/fuel ratio of the exhaust flowing therein is convergent, the step of judging whether E_(DT)−E_(DU)<E_(A)−(L_(U)−g) is established or not is carried out.
 15. The method as claimed in claim 14, wherein the step of judging whether the temperature of the exhaust emission purifier or the air/fuel ratio of the exhaust flowing therein is convergent or not, includes a step of judging whether at least one of the temperature of the exhaust emission purifier and the change rate thereof is within a predetermined range or not, or whether at least one of the air/fuel ratio of the exhaust flowing in the exhaust emission purifier and the change rate thereof is within a predetermined range or not.
 16. The method as claimed in claim 10, wherein when the sum of a detection error of the air/fuel ratio and a detection error of an air-intake amount is less than the maximum tolerance, the step of judging whether E_(DT)−E_(DU)<E_(A)−(L_(U)−g) is established or not is carried out.
 17. The method as claimed in claim 10, further comprising a step of judging whether an amount of HC passing through the exhaust emission purifier has a value equal to or less than a predetermined value, and when it is judged that an amount of HC passing through the exhaust emission purifier has a value equal to or less than a predetermined value, the step of judging whether E_(DT)−E_(DU)<E_(A)−(L_(U)−g) is established or not is carried out.
 18. The method as claimed in claim 10, further comprising a step of judging whether a value E_(T)/ΔT_(C) obtained by dividing a detection temperature error E_(T) of the exhaust emission purifier by the rate ΔT_(C) of temperature increase of the exhaust emission purifier per unit time is smaller than the maximum tolerance E_(A) or not, and when it is judged that E_(T)/ΔT_(C)<E_(A) is established, the step of judging whether E_(DT)−E_(DU)<E_(A)−(L_(U)−g) is established or not is carried out.
 19. The method as claimed in claim 18, further comprising a step of judging whether an amount of HC passing through the exhaust emission purifier has a value equal to or less than a predetermined value and, only when it is judged that an amount of HC passing through the exhaust emission purifier has a value equal to or less than a predetermined value, the step of judging whether E_(T)/ΔT_(C)<E_(A) is established or not is carried out. 